Only add LookbackDelta to vector selectors (#4399)
Only add LookbackDelta to vector selectors (#4399)

Signed-off-by: Thomas Jackson <2d00bc2c74768cf27c5a78623e81f1b7f1ca2826@gmail.com>

Related to #4226
keegancsmith/prometheus,prometheus/prometheus,alileza/prometheus,prometheus/prometheus,Gouthamve/prometheus,kangwoo/prometheus,prometheus/prometheus,GoogleCloudPlatform/prometheus,kangwoo/prometheus,GoogleCloudPlatform/prometheus,Gouthamve/prometheus,prometheus/prometheus,prometheus/prometheus,GoogleCloudPlatform/prometheus,alileza/prometheus,kangwoo/prometheus,keegancsmith/prometheus,alileza/prometheus,keegancsmith/prometheus,Gouthamve/prometheus,GoogleCloudPlatform/prometheus,GoogleCloudPlatform/prometheus,Gouthamve/prometheus,kangwoo/prometheus,alileza/prometheus,alileza/prometheus,keegancsmith/prometheus,keegancsmith/prometheus